Axial columns with packed beds of particles are commonly used both in process scale chromatography and in solid-phase synthesis of e.g. peptides or oligonucleotides. In chromatography, the bed contains adsorbent particles for selectively binding and certain feed components and in solid phase synthesis the particles used have suitable reactive groups for stepwise synthesis of the peptide or oligonucleotide, In such columns, the packed particle bed is usually stabilized by compression in an axial direction using a piston (which can alternatively be called an adaptor). The compression force may be applied to the piston via e.g. a threaded rod or a hydraulic jack, but it can also be applied by the introduction of a hydraulic liquid into a hydraulic chamber A confined between the top B of the piston and a top cover C of the column, as shown in FIG. 1. This arrangement has been described in e.g. U.S. Pat. Nos. 5,021,162, 6,280,616 and WO2004/103517. Such columns are also commercially available, e.g. as FineLine or InDex columns from GE Healthcare Bio-Sciences AB (Sweden).
To avoid contamination, the hydraulic liquid is usually selected to be identical to or similar to the liquids applied to the bed in the chromatographic separation process/solid phase synthesis. In chromatography this can mean a wide range of liquids, from water (usually with 20% ethanol added as a preservative) to alcohols, acetonitrile etc, while in solid phase synthesis, acetonitrile and toluene are commonly used. Many of these liquids are both toxic and flammable, so it is highly desirable to contain them in closed systems and to avoid spillage and the formation of explosive vapour-air mixtures.
After finishing a separation campaign on a chromatography column and after finishing a synthesis on a synthesis column, the column is normally disassembled in order to remove the packed bed, clean the column and to introduce a new packed bed. In order to do this, the hydraulic fluid first has to be removed from the hydraulic chamber. Typically this is done by introducing a drainage tube D in the chamber and pumping out the liquid, e.g. by using a peristaltic pump. A significant amount of liquid will however remain in the chamber, which poses a health and explosion hazard when the column is disassembled.
Removal of liquid can also be an issue in columns which do not have a top cover above the piston. Spillage of buffers and other liquids onto the top of the column is common in process settings and these need to be removed for safety, hygiene and/or corrosion prevention reasons. On large columns, which can be up to 2 m or more in diameter, it is difficult to remove all liquid from the piston.
Accordingly there is a need for pistons, columns and methods that allow complete or essentially complete removal of liquid from the hydraulic chamber and/or the piston top side and particularly without causing exposure to vapours.